There are valve mechanisms having a swing rocker arm in which a pressing portion that presses a valve is provided at its tip end, and the rear end of the swing rocker arm is swingably supported. Among such valve mechanisms, there are valve mechanisms in which the rocker arm has a double structure formed by a main arm and a sub arm, and the valve is switched between the driven state and the stopped state or the working angle (lift amount) of the valve is switched by coupling and decoupling the sub arm to and from the main arm, as shown in Patent Literatures 1 to 6.